This invention relates to varactor tuning systems of the type described in a copending application entitled "Digital Tuning System With Programmable Memory", Ser. No. 684,339, by Daniel Heuer and Arthur N. Borg, filed May 7, 1976, now abandoned, hereby incorporated by reference. Specifically, an apparatus for selecting a desired television channel from a keyboard is described.
Varactor tuners are known in the art and numerous tuning systems have been developed for supplying a control voltage for tuning a desired station. Some of these systems are sequentially tuned whereby a depressed switch causes the tuner to tune through the tuning band. When the desired station is reached, the operator releases the switch.
It is, however, desirable to allow an operator to directly select a station by selecting two digits on a keyboard. In tuning systems which utilize a channel memory containing tuning information for the varactor tuner, a keyboard has been used to directly address a memory producing a desired channel tuning. This direct access to the memory containing tuning information by the keyboard is inflexible in that each channel must be preassigned a memory address. The memory in tuning systems of this type is dedicated, i.e., each memory cell will be required to be assigned specific channel tuning information. The operator when selecting a channel number selects a memory address rather than directly selecting a channel number to be tuned.
The present invention does not require direct address to a tuning memory but rather depends upon the detection of a difference between a channel selected and an indication of a presently tuned channel for initiating tuning.